It is possible that the you have created a group with a task assigned to a user in it. But the access rights within this group are not configured correctly and this user does not have access to this task. To correct it, please go to Workgroups > More > Edit Settings > Tasks

Please check, whether this new user is a full-fledged invited user on your account. Please go to "Company" main menu tab>Employees> Invited, Employees menus. Also, it is possible that this task may be attached to a CRM entity, such as Lead, Contact, etc., then your user should have CRM Access Permissions granted to him/her. If access problem still persist, please submit a detailed query to our HelpDesk for further investigation.

I sent him an invite, he accepted it, and is now showing as an employee.I simply created the tasks and assigned it to him, that's it. I did not do anything special or attach them to anything. I assumed that this was all that was required when creating a task, as that is how it has worked with all other PM systems I have used, but it seems there some more convoluted process involved with Bitrix when creating a task and assigning it to somone? Can you please let me know all the steps required to add a task and assign it to someone so that they can use the task, update it, add notes, and close it when complete.